This invention relates generally to UHF antennas and particularly to UHF antennas that are intended for indoor use. With the recent adoption of television signal transmission standards for HDTV (High definition television) signals and ATSC (Advanced television systems committee) type signals, the need for significantly improved UHF antennas, primarily for indoor use, has become apparent. Since the transmitted signals are digital, it is imperative that signal reception be optimized to prevent data corruption.
Conventional UHF indoor antennas are limited in gain and very sensitive to the direction and polarization of the received signals. In an analog environment, signal reflections and reduced gains were more tolerable in that the quality of the picture was compromised, but at least the viewer was presented with a compromised, but viewable picture. With digital signals, these same signal impairments most often result in no viewable picture. Further, the transmitted digital signals are of much lower power than their analog counterparts (to minimize interference into cochannel NTSC signals) and it is very important to maintain a high signal to noise ratio.
The UHF antennas of the invention include a reflecting backplate and an increased width/length ratio. The increased width/length ratio improves the wideband performance of the antenna, whereas the reflector guarantees a 10 to 15 dB front to back ratio in addition to providing excellent decoupling between the output cable and the dipole elements. Additionally, the dipole plates are supported by support stubs that maintain an approximate .lambda./4 distance between the reflector and the dipole elements. (Those skilled in the art will recognize that .lambda. is the free space wavelength of the UHF band center.) Both passive and active antennas are disclosed. The active antennas include amplifiers and may be oriented for vertically polarized signals, horizontally polarized signals or both such types of signals.